Debris from the crash was found at about 1 a.m. in Browns Bay, just north of Edmonds and about eight miles north of Seattle. Edmonds police Sgt. Jeff Jones said papers and pieces of the helicopter found floating about a mile offshore identified the aircraft.

It was apparent from the size of the debris field, about a quarter-mile wide and a half-mile long, that none of the three crew members survived, Jones said.

The cause of the crash was not immediately known, he said.

Jones said the helicopter apparently sank in 300 feet of water. The U.S. Coast Guard kept a boat at the scene overnight, and search efforts were to resume at daylight.

The helicopter left the Seattle hospital at 9:04 p.m. and was expected to arrive at its home base in Arlington at 9:19 p.m., but it never arrived, said Coast Guard Petty Officer Jason Koelle.

Dispatchers at Airlift Northwest contacted the pilot at 9:14 p.m., the Seattle-based company said in a statement. When it tried 10 minutes later, dispatch could not reach the pilot. A pilot and two nurses were on board the Agusta 109 helicopter.

A resident in the 8400 block of Talbot Road in Edmonds called 911 and reported that a helicopter flew over the house near Browns Bay and it "didn't sound right," said Edmonds Police Sgt. Jeff Jones; the resident then heard an explosion and didn't hear the helicopter anymore.

A Coast Guard helicopter and boat were dispatched to help with a search, said Petty Officer Kurt Fredrickson.

At least two Airlift Northwest helicopters have crashed in Western Washington in recent years.

An Agusta A/109 helicopter crashed in the Cascade town of Baring in 2002 when both of its engines failed.

A pilot and two nurses died in a 1995 crash off Bainbridge Island when the helicopter ambulance was flying from Seattle to pick up a patient. The National Transportation Safety Board ruled that pilot error likely caused that accident.